1. Technical Field
This disclosure relates to semiconductor fabrication and more particularly, to an improved method for releasing semiconductor wafers from a polish pad.
2. Description of the Related Art
Semiconductor processing includes polishing semiconductor wafers. Typically, semiconductor polishing includes chemical mechanical polishing or CMP. For polishing, semiconductor wafers are typically placed on a polishing pad. A platen supports the polishing pad during processing. The wafer is placed on the platen having the polishing pad disposed thereon using a mechanical carrier. The platen often provides rotation for polishing the wafer. In addition, the carrier rotates as well. During polishing, a slurry is introduced onto the polishing pad which includes abrasive materials, such as silicon dioxide particles as well as chemicals for etching the surface of the wafer to provide a polished surface on the wafer. The polishing pad includes pores to carry the slurry and distribute the slurry over the wafer.
The slurry or slurries typically used have high viscosities. At the end of polishing, the carrier removes the wafer from the polishing pad to be cleaned or simply unloaded. The slurry viscosity can make the removal of the polishing pad from the wafer difficult since the slurry viscosity causes the polishing pad to stick to the wafer. If the wafer sticks to the polishing pad, this may result in dropping the wafer and cause damage to or even break the wafer. Further, the viscosity of the slurry may cause the wafer to remain in contact with the polishing pad while the carrier attempts to remove it. This may also result in damage to or breakage of the wafer.
Referring to FIG. 1, a carrier 10 is shown for polishing a wafer 12. Wafer 12 is releasably coupled to carrier 10 such that wafer 12 may be removed therefrom without damaging wafer 12. Carrier 10 is moved in the direction of arrow "B" to bring wafer 12 into contact with a polishing pad 14. Polishing pad 14 is disposed on a platen 16. Platen 16 may include a turntable for providing a mechanical polishing motion for polishing wafer 12 as will be described herein.
Referring to FIG. 2, after contacting polishing pad 14, wafer 12 is rotated by carrier 10 as indicated by arrow "A". In addition, platen 16 is rotated in the direction of arrow "C" thereby providing mechanical polishing when abrasives included in slurry 18 are introduced on polishing pad 14. Slurry 18 preferably includes silicon dioxide or aluminum oxide abrasives having a primary particle size of about 100 A an up. Slurry 18 is introduced gradually from a slurry feed 20 onto polishing pad 14. A pressure P is applied to carrier 10 to provide a normal force to assist in polishing wafer 12.
Referring to FIG. 3, toward the end of the polish, slurry 18 is no longer introduced to polishing pad 14. A water polish step is introduced in which water 22 is introduced onto polishing pad 14. Depending on slurry viscosity, platen 16 is rotated in the direction of arrow "C" at a rate of about 50 rpm's for about 1-60 seconds prior to carrier 10 separating wafer 12 from pad 14. However, slurries usually have a high viscosity and the introduction of water is not sufficient to provide adequate separation from polishing pad 14.
Damage to the wafer reduces throughput, and any delay in cleaning the wafer which may result due the difficulty in removing the wafer from the polishing pad may also result in a reduction of wafer yield. Therefore, a need exists for a method for enhancing wafer release from a polish pad after a polishing step.